1. Field of the Invention
The present invention relates to liquid crystal device and manufacturing method for the same.
2. Description of the Prior Art
Liquid crystal devices have been broadly used. Particularly, due to their light weights and small sizes, many compact electric appliances such as compact electric calculators, watches, lap-top word processors and pocket television systems are provided with liquid crystal displays.
The driving circuit of such a liquid crystal display has been formed in a separate printed board made of a glass epoxy substrate in which a semiconductor device such as a packaged IC is mounted. The electric connection is made through FPC (Flexible Print Circuit) between the printed board and inner electrodes formed in the insides surfaces of a pair of substrates in which a liquid crystal is disposed.
Recently, TAB (Tape Automated Bonding) has been employed to make electric connection. In accordance with this method, semiconductor chips provided with solder bumps on their contact pads are mounted on and electrically connected with Cu electrodes formed on a polyimide film by face-down bonding (ILB: Inner Lead Bonding), and then electrode strips formed on the substrates of a liquid crystal display are coupled respectively with counterpart electrode strips of the polyimide film (OLB: Outer Lead Bonding).
The IC chips can be mounted directly on the substrates of a liquid crystal display. In this case, an electric circuit pattern for supplying driving signals to electrode strips of the substrates defining pixels of the liquid crystal display and control signals to the chips has to be formed in advance. The IC chips are connected to the pattern by means of Au wiring or bumps attached to the contact pads of the chips.
There are some shortcomings, however, in the above conventional technique. In the case using a glass epoxy board, the advantage of light weights claimed by liquid crystal display is largely diminished because of the heavy board. Furthermore, the use of the intermediary FPC is undesirable. There are two sites of connection at both ends of the FPC and therefore the frequency of occurrence of connection error is doubled. The difference between the FPC and the glass substrates of a liquid crystal display in thermal expansion coefficient becomes a cause of stress at the connection. This problem is also the case at the connection made in accordance with the TAB method. In addition, polyimide tape is expensive. In the case of the direct mounting of IC chips, the yield of production is the product of the yield of liquid crystal panel and the yield of the driving circuit and therefore the decrease of the whole yield is substantial.